Statistically, the industrial sector generally accounts for 38% of the total energy consumption, within which the combustion devices take on about 70% of the energy consumed by the industrial sector. Therefore, the increasing in the combustion efficiency of the combustion devices can be the most beneficial way to save energy consumption.
Generally, there are two types of heating devices being used in industrial manufacturing processes, which are combustion devices and electrical heaters, such as boilers, melting furnaces, furnace, heat treatment furnace, forging furnace, blast furnaces, kilns, and so on. Among those, the most common heating devices that are used are the combustion devices. However, the combustion devices can't operate without the help of electrical peripheral devices, including: blowers, pumps, and control circuits, etc. Thus, for a combustion device to operate smoothly, it is required to be provided with fuel and elecytricity at the same time. Therefore, from the user's point of view, the means for fuel saving and electricity saving should be adopted simultaneously so as to minimizing energy expense in the combustion devices and thus enabling the econimic efficiency to be maximized for the whole industrial manufacturing process using the combustion devices.
In combustion devices, combusion is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, and often gaseous products, including natural gas, diesel and heavy oil. The heat resulting from the combustion is then used for heating water or a raw material to a designated temperature for melting, boiling, evaporating, or other heat treatment processes. Nevertheless, after reaching the designated temperature, the excess heat from the combustion is generally recycled by the use of a heat recycling device while allowing some to be wasted in a form of hot flue gas or radiation. Overall. The energy utilization rate for a combustion device is depended on the quality of the combustion condition and the heat utilization in the manufacturing process, while the excess heat is usually dissipated or discharged. Thus, the energy loss in an operating combustion device can be the result of imcomplete combustion, waste heat discharging, or heat dissipated from the low-temperature insulation walls and piping in the combustion system. Among which, the imcomplete combustion not only can cause fuel value loss in a manufacturing process, but also it can cause more pollutants to be generated, such as CO, SOx, NOx, and powders emission, and thus more related issues can be caused, including air pollution and dirty contaminated equipment. On the other hand, the dissipation of excess heat is more than just waste in thermal energy, it can also cause a sort of heat pollution in the general working area of the combustion device, while eventually causing higher electric bill to be spent for air conditioning.
Hydrogen that is used as fuel had already been proven to be advantageous in fuel consumption reduction and reducing pollutant reduction in exhaust. Taking the generator that uses methane as fuel for example, its CO2 emission can be effectively reduced after dosing a small amount of hydrogen, ex. 10% vol, into methane at a specific condition that will enables the combustion efficiency to be significantly increased by about 20%, and thus the fuel consumption can be reduced significantly. As fuel can account for about 90% in the whole operation cost for a common combustion device, any kind of saving in fuel consumption can be a great help for cost saving. Therefore, exactly how must cost can be saved depends upon the accessibility of hydrogen, i.e. the means for generating and obtaining hydrogen. It is noted that the majority of hydrogen on Earth exists in a form of compound, such as water, and only a few exists in reduced form. Therefore, it is common to access hydrogen using an artificial means, whereas the most common artificial means for producing hydrogen includes: hydrogen production as byproduct in crude oil pyrolysis, hydrogen production as byproduct in a chemical industry and hydrogen production in water electrolysis. Among which, in crude oil pyrolysis, hydrogen is produced mainly in the reforming reaction process, where the mixture of hydrocarbon and water is decomposed at a high temperature into oxycarbide and hydrogen with a certain amount of carbon deposition. As water electrolysis is enabled by electricity and is the decomposition of water into oxygen and hydrogen due to the conduction of an electric current through water, which can be a clean and simple procedure. Comparing to the hydrocarbon reforming process which will inevitably casue some carbon emission, the electrolysis is a process of zero-carbon emission. Nevertheless, if the electricity used for powering the electrolysis is generated by a fossil fuel burning power plant, it is difficult to say that such electrolysis is zero-carbon emission and even that the carbon emission may not be less than the reforming reaction process in crude oil pyrolysis.
In addition to the difference in the use of different energy sources, the difference between the reforming reaction process in in crude oil pyrolysis and the water electrolysis is that: the byproducts of the reforming reaction process in in crude oil pyrolysis is mainly composed of hydrogen and carbon dioxide with a small amount of carbon monoxide, while the products of the water electrolysis are only hydrogen and oxygen. It is noted that combusion is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant that are mixed into a mixture with a specific concentration. Without containing any oxygen, the hydrogen-rich gases that are produced from the reforming reaction process in in crude oil pyrolysis can be transported safely without any combustion hazard before entering into the combustion chamber if the transportation circuit is properly sealed and the flow speed is well controlled. On the other hand, although the hydrogen being produced by water electrolysis can also be safely transported if its transportation circuit is properly sealed and the flow speed is well controlled, such hydrogen transportation is still more hazardous comparing to those in crude oil pyrolysis since there is oxygen existed simultaneously with hydrogen. Moreover, as the reforming reaction process in in crude oil pyrolysis is a high-temperature catalytic reaction, it is enabled by external heating so that the waste heat from the combustion device can be recycled and used for triggering such reforming reaction process. Thus, the cost for hydrogen production can be greatly reduced comparing to the electrical water electrolysis.
Although the effectiveness of hydrogen-assisted combustion had been proven and there are already a variety of hydrogen production processes available, there is little practical cases existed due to safety concerns in hydrogen usage or the lack of information about how to obtain hydrogen. Therefore, there is little industry had actually adopt the hydrogen-assisted combustion means.
The waste heat recycle means is a mature technique used in conventional turbine generators. However, as the operation temperature for recycling waste heat in those turbine generators is generally higher than 300° C., such waste heat recycling technique cannot be adapted for other heat sources that are lower than 300° C. Nevertheless, considering the increasing power demand, low-temperature waste heat recycling technique below 300° C. is becoming more and more ergently needed despite that most industrial waste heat temperatures are lower than 300° C. The low-temperature waste heat recycling technique below 300° C. whose effectiveness had already been proven includes: the Organic Rankine Cycle (ORC) and the related techniques, and the Thermoelectric Power Generation (TEG). The Organic Rankine cycle (ORC) is named for its use of an organic, high molecular mass fluid with a boiling point, occurring at a lower temperature than the water-steam phase change. The working principle of the organic Rankine cycle is the same as that of the conventional generator, but it requires larger working area and is suitable for high-volume power plants that generate more than 100 kW. On the other hand, the TEG is a solid state device that converts heat (temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect (a form of thermoelectric effect). Thermoelectric generators function like heat engines, but are less bulky and have no moving parts, so that it can be adapted for low-volume power plants that generate less than 100 kW. However, TEGs are typically more expensive and less efficient. Nowadays, the ORC and TEG can both be found in various industrial waste heat recycling applications.
Form the above description, the current operation condition of conventional combustion devices can be concluded as following: there is a great amount of waste heat in the exhaust flue gas being discharged from the combustion devices; the incomplete combustion is common in the conventional combustion devices, so that the operation of the conventional combustion devices can cause high pollution; the air-fuel ratio in those conventional combustion devices is limited within a specific range; the peripheral devices for the conventional combustion devices are operating with high power consumption; and there is little and slow progress in the improvement of the conventional combustion devices. Consequently, the conventional combustion devices have the following disadvantages: high energy waste; the heat recycling devices for the conventional combustion devices can be easily damaged; the exhaust flue gas of the conventional combustion devices can cause high environmental pollution; the operation of the conventional combustion devices can easily generate a high volume of NOx, with high heat loss. Therefore, it is in need of an integrated combustion device power saving system capable of recycling waste heat to be used as power source for generating hydrogen in the reforming reaction process of crude oil pyrolysis, while allowing the generated hydrogen to be used for assisting and improving the combustion efficiency of the integrated combustion device; or recycling waste heat and converting heat (temperature differences) directly into electrical energy so as to be provided and feedbacked to the integrated combustion device. Thereby, the fuel consumption is reduced, the waste flue gas quality is improved, the lifespan of the heat recycling device is prolonged, and the integrated combustion device can act as a power generator itself for reducing its dependence upon external power grid.